Step 1: pick the fan mode
The Mode setting tells the ECU what kind of fan it's controlling.
| Mode | Fan type | How it's driven |
|---|---|---|
| Digital - Switched | Plain on/off fan | An output switches it fully on or off |
| Digital - Duty Cycle | Variable speed fan | A PWM duty signal sets fan speed |
| CAN - Switched | On/off fan | Commanded over CAN |
| CAN | Variable speed fan | Speed commanded over CAN |
Variable speed control is worth having if your fan supports it. The fan runs only as hard as it needs to, which is quieter, easier on the charging system and holds coolant temperature steadier than cycling on and off.
Step 2: choose the output
Set the Thermo Fan Output. The rule is simple: the ECU can only power the fan directly from a 25A HCO (High Current Output). Any other output must go through something that can handle the current.
- Driving it directly: use a 25A HCO. For Digital - Duty Cycle this is the recommended setup.
- No 25A HCO free, switched fan: use a DPO (or another spare output) to trigger a relay that powers the fan, like a 30A 5-pin power relay.
- No 25A HCO free, PWM fan: a regular mechanical relay can't be pulsed at PWM speeds, so trigger a solid state relay from a DPO instead, such as the 100A solid state relay.
If you're running Digital - Duty Cycle straight from a 25A HCO, enable Soft Start on that HCO. Fan motors pull a big current spike at startup, and ramping them up gently is easier on the output, wiring and fuse.
Step 3: optional override input
The Thermo Fan Override Input lets a switch force the fan on, which is handy for cooling down after a track session or in slow traffic on a hot day. Any spare AVI or SPI works for it.
Checks before you rely on it
- Use wire and a fuse sized for your fan's current, not just the ECU output rating.
- Test the output from NSP and confirm the fan actually runs, and for PWM, that speed changes with duty.
- Log coolant temperature and fan output on a hot day before calling it done.
Once it's wired, set the on and off temperatures in Thermo Fan and shape PWM fan speed in Thermo Fan Duty Cycle. Not sure your fan's current draw suits your ECU's outputs? Ask us.
